Process for producing high performance crimped rayon staple fiber

ABSTRACT

Highly crimped, high tenacity rayon filaments and staple fibers are produced by spinning a viscose spinning solution containing a mixture of modifiers and having a low viscose salt (NaCl) index, into a coagulating-type spin bath to obtain coagulated, incompletely regenerated viscose filaments. The coagulated viscose filaments are withdrawn from the spin bath and stretched up to about 120 percent in length while the filaments are still substantially soluble in dilute alkali solution. The filaments are then completely regenerated and the tension is relaxed to produce highly crimped filaments or staple fiber products which are finished by conventional washing, desulfurization and finishing techniques.

Stevens et a1.

1 PROCESS FOR PRODUCING HIGH PERFORMANCE CRIMPED RAYON STAPLE FIBER [75] Inventors: Hugh Dexter Stevens, Long Valley;

Thomas Emery Muller, Springfield, both of NJ.

[73] Assignee: International Telephone and Telegraph Corporation, New York, N.Y.

[22] Filed: Oct. 20, 1970 [21] Appl. No.: 82,485

[52] U.S. Cl. ..264/168, 264/188, 264/193,

[51] lnt.Cl. ..D0lt 3/12, DOld 5/22 [58] Field of Search ..264/168, 188-198 [56] References Cited UNITED STATES PATENTS 2,347,883 5/1944 Cox ..264/168 2,347,884 5/1944 Cox ..264/168 2,941,938 12/1949 Schlosser et a1 ..264/168 2,364,273 12/1944 Cox ..264/168 2,515,834 7/1950 Nicoll ..264/168 2,515,889 7/1950 Nicoll ..264/168 2,852,333 9/1958 Cox ..264/168 1March 13, 1973 Primary Examiner.lay H. Woo

Att0rneyC. Cornell Remsen, Jr., Walter J. Baum, Paul W. Hemminger, Charles L. Johnson, Jr., Delbert P. Warner, Marvin M. Chaban and James B. Raden [57] ABSTRACT Highly crimped, high tenacity rayon filaments and staple fibers are produced by spinning a viscose spinning solution containing a mixture of modifiers and having a low viscose salt (NaCl) index, into a coagulatingtype spin bath to obtain coagulated, incompletely regenerated viscose filaments. The coagulated viscose filaments are withdrawn from the spin bath and stretched up to about 120 percent in length while the filaments are still substantially soluble in dilute alkali solution. The filaments are then completely regenerated and the tension is relaxed to produce highly crimped filaments or staple fiber products which are finished by conventional washing, desulfurization and finishing techniques.

5 Claims, No Drawings PROCESS FOR PRODUCING HIGH PERFORMANCE CRIMPED RAYON STAPLE FIBER This invention relates to the production of new and improved highly crimped high tenacity rayon filaments and staple fibers. More particularly, it relates to methods for spinning highly crimped, high performance rayon filaments and staple fibers combining a high degree of orientation with a spinning balance allowing the development of chemical, permanent crimp.

In the past, high performance, high wet modulus rayon filaments and staple fibers have been developed which are suitable for use as such in fabrics or in blends with synthetics. In the course of continued research effort in the area of high performance viscose rayon, we have found a new and improved method for producing new types of crimped high performance, high wet modulus rayon filaments and staple fibers which can be used along or in blends, for example, with cotton, wool, synthetic fibers such as acrylics, polyesters, nylon and the like. These new rayon products have excellent physical properties which make them adaptable for good processability. An especially important characteristic of these new products is their superior resistance to caustic soda resulting from the high degree of polymerization of the fibers and the high degree of orientation of their crystalline structure. These new fibers are chemically crimped and the resulting crimp is completely stable, meaning that rewetting and subsequent redrying of the fibers results in no loss of the crimped character of the fibers.

The fibers of this invention are well suited for durable press and soil release resin treatment and show good dimensional stability in laundering and in Sanforizing. Their reduced caustic solubility is a significant advantage in textile processes which involve use of caustic soda, such as mercerization. The fibers are tougher than lower elongation rayons and have superior durability and wear resistance.

Heretofore, various methods have been proposed for the preparation of crimped rayon filaments and fibers. For example, methods are known for producing crimped regular (low wet modulus) rayon. However, such regular or unmodified rayon has relatively low orientation which does not permit realization of spinning stretch levels in excess of about 50%. These crimped regular rayon fibers normally have relatively low conditioned and wet tenacities and low wet modulus (i.e., wet tenacity at 5 percent elongation).

in preparing crimped, highly oriented, high wet modulus rayon, special problems are encountered as opposed to crimping of regular rayon. Known procedures for producing crimped high performance rayon filaments and staple fibers have required special spinning equipment, or special processing procedures such as formaldehyde modification of the fibers, or extra processing and after-treatment steps to create the necessary imbalance in the system to produce such a crimped fiber. It should be clear that such special equipment and techniques and such added processing stages are costly, and can be time consuming and relatively inefficient.

Therefore, it is an object of the present invention to provide methods for producing new and improved high performance crimped rayon filaments and staple fibers.

In this regard, it is an object to provide economical and efficient methods for the production of these crimped fibers.

A further object is to provide methods for developing high frequency macro and microcrimps in a high wet modulus rayon without requiring special spinning equipment, formaldehyde modification of the fibers, or added processing and after-treatment steps in the process.

Another object is to provide new and improved high performance crimped rayon filaments and staple fibers having adequate strength, elongation and dimensional stability to enable good processability and, further, having superior resistance to caustic soda.

Additional objects, if not specifically set forth herein, will be readily apparent to those skilled in the art from the following detailed description of the invention.

Generally, the process of the invention comprises preparing a viscose solution from cellulose xanthate having a relatively high degree of polymerization (D.P.). This, viscose solution contains a mixture of modifiers and has a relatively low viscose salt index. The spinning of the viscose is conducted at a higher than normal temperature in a low acid concentration, coagulating-type spin bath containing metallic salts to effect coagulation. It should be noted that the spin bath contains no formaldehyde therein.

While the filaments are in a state of coagulation and are still incompletely regenerated, the viscose filaments are stretched the desired amount, normally not greater than about [20 percent and usually about percent. The number of stages of stretching can be varied as desired, but the stretching should be started at an early stage, preferably while the filaments are still in or close to the primary spin bath. The greater proportion of stretching is achieved prior to substantial regeneration of the filaments However, the stretching can be continued during passage of the filaments through a hot secondary regeneration bath, if desired. Before the tension on the filament is relaxed, regeneration is substantially completed and the regenerated filaments are washed. Thereafter, the filaments, or staple fibers prepared therefrom, are subjected to conventional desulfurization and washing and the resulting highly crimped filaments or staple fiber products are finished under conditions which are balanced to preserve crimp, high modulus and high strength, while providing adequate elongation for good conversion properties and good wear and abrasion-resistance in the endproducts.

High D.P. modified viscose spinning solutions suitable for use in the process of the present invention are prepared from cellulose xanthate having a relatively uniform chain length with a DP. of from about 350 to 600, a suitable balanced ratio of cellulose and sodium hydroxide within the range of about 4 to 9'percent in the viscose and from about 32 to 40 percent carbon disulfide (based on 0D. cellulose). In the process, purified chemical cellulose such as bleached sulfite or prehydrolyzed kraft wood pulps as well as cotton linters having relatively high DJ. and uniform D.P. distribution are converted into alkali cellulose and xanthated with 32 to 40 percent carbon disulfide, usually 34 to 38 percent carbon disulfide will be sufficient, at close to ambient reaction temperatures (e.g., 20-30 C) in the conventional manner.

The viscose is modified with a mixed modifier. A variety of viscose modifiers may be used for this purpose and they may be added to the dissolver or injected just prior to spinning. For dissolver addition, polyethylene glycol (PEG) or similar compounds may be added with the caustic charge. Dimethylamine (DMA) or similar amines are usually added after about two-thirds of the mixing cycle has been completed. A low mixing temperature (e.g., about C) has been found to improve solution quality and minimize loss of the relatively volatile amine modifier. In a preferred embodiment of our invention, the mixture of modifiers comprises from about 0.5 to 2.5 percent dimethylamine (DMA) and from about 0.5 to 2.5 percent polyethylene glycol (PEG) based on the the weight of the cellulose.

The viscose should be fully deaerated. This complete deaeration is important in the process since it prevents filament breakage while attaining the desired stretch and high degree of uniaxial orientation during spinning.

Contrary to prior art high wet modulus spinning systems in which the salt (NaCl) index is usually from about 6-12 or higher, we have found that the salt index of the spinning solution employed in our inventive process should be kept low, preferably between about 2.5-6, to obtain a spinning chemistry balance favorable to a high degree of crimping. Normally, a spinning solution having a low salt index indicating a high degree of ripening of the modified viscose would be expected to provide a product with a low wet and conditioned tenacity and a much reduced wet modulus. Surprisingly, by employing the critical combination of processing variables which we have discovered, the crimped rayon filaments and staple fibers produced from these spinning solutions having relatively low salt indexes, have been found to possess high conditioned tenacity, high wet modulus, high wet tenacity, and good elongation. The filaments and fibers of the invention have an average conditioned tenacity of 3 to 4 g.p.d., a wet modulus of 0.4 to 0.6 g.p.d., a wet tenacity of 2 to 3 g.p.d., a conditioned elongation of 10 to percent and a wet elongation of 12 to 18 percent. In addition, the filaments and fibers have a solubility in 6.5 percent sodium hydroxide solution at 20 C of about 8 percent by weight and have a water retention of from 70 to 100 percent. Furthermore, we have found that the crimped fibers of the invention exhibit excellent single fiber flex resistance indicating the toughness and resistance to wear of the fibers.

The viscosity of the spinning solution is not particularly critical and can range between about 80 to 140 ball fall seconds (b.f.s.) measured at 20 C. This is an advantageous viscosity level since most processes for spinning high tenacity filaments require higher viscosities (up to about 400 b.f.s.) to produce satisfactory high tenacity fiber. High viscosity makes accurate denier control difficult and interferes with deaeration, pumping and spinning processes.

In the process of the present invention, the modified spinning solution is spun at a take-up seed of 30 to 50 meters per minute into a coagulating-type spin bath at a temperature of about 35-45 C which is higher than usual for high wet modulus spinning. The spin bath contains a relatively low acid concentration (e.g., about 4 to 6 percent sulfuric acid), 1 to 6 percent zinc sulfate and from 10 to 20 percent sodium sulfate. The

spin bath may also contain an amount of a surface active agent or lubricant, such as lauryl pryridinium chloride (LPC) and the like, sufficient to produce a surface tension of 40-50 dynes per centimeter. It should be noted that selection of a proper balance in primary spin bath acid level and temperature is an important factor in our inventive process.

Travel of the filament through the primary spin bath should be limited to that required to develop sufficient strength for stretching in order to avoid any unnecessary regeneration, with the greater percentage of stretch achieved prior to substantial regeneration. To effect this stretch, the tow is drawn from the bath the desired distance, passed several times around a driven godet and then several times around two or more godets driven at a sufficiently greater speed to provide the desired continuous stretching.

Since filaments made by the procedures described above are highly plastic and relatively strong immediately upon extrusion into the coagulation bath, it is important to stretch as quickly and as much as possible prior to regeneration in order. to obtain the desired high wet modulus. The strongest filaments with the highest wet modulus are produced when the stretching takes place immediately after the onset of coagulation in a gradual fashion. For example, when only two stretch rolls are used, most of the stretching occurs on or as the tow leaves the first roll. The stretching is then completed as the tow of filaments passes through the air in contact with adhering spin bath on its way to and through the regeneration bath or baths.

To regenerate the coagulated filament tow, it is conducted through one or more hot regeneration baths which may contain either hot dilute acid or steam. While steam baths can be used we prefer dilute acid baths for our purpose of 60 to 100 C (preferably about 98 C) containing from about 0.5 to 5.0 percent sulfuric acid (preferably about 3.0 percent) and a stabilized modicum of the salts carried over from the the preceding coagulation bath. During regeneration, the filament receives the balance of the total stretch.

After the filaments are completely regenerated, tension is removed to permit crimp development. Following relaxation, the filaments are acidified, desulfurized, neutralized, washed, finished and dried by conventional techniques.

Alternatively, the filaments can be cut into staple fibers which develop a high degree of crimp on relaxation. These highly crimped staple fibers are acidified, desulfurized, neutralized, washed, finished and dried by conventional techniques. Cutting of the tow into staple fibers is usually performed in the acid state.

The finishing of the crimped filaments and staple fibers should be balanced to preserve crimp, high modulus and high strength, while building adequate elongation for good conversion properties and good wear and abrasion-resistance in end-products. Use of a commercially available staple fiber finishing agent is advantageous to insure processability for efficient conversion to yarn and fabric.

The following examples are set forth for the purpose of illustrating the method of this invention and the characteristics of the resulting products only and are not intended to be construed as being limitative in any respect.

EXAMPLEl A modified viscose spinning solution was produced from alkali-treated chemical cellulose which was prepared by steeping a high purity of 1050 DP wood pulp having. uniform chain length distribution in 18.6 percent sodium hydroxide at 25 C. The thus formed alkali cellulose contained, after pressing, 35 percent cellulose and 15 percent sodium hydroxide. The alkali cellulose was shredded and aged to a DP of about 450. It was then reacted with 35 percent carbon disulfide, based on the weight of cellulose, at 26 C to form cellulose xanthate which was dissolved in sodium hydroxide at C and mixed for 2 hours to produce a viscose solution containing 7.5 percent cellulose and 7.5 percent sodium hydroxide. To this viscose solution, 1.0 percent dimethylamine and 1.0 percent polyethylene glycol (both based on weight of cellulose) were added. The viscose solution was ripened to a salt (NaCl) index of 4.5.

The well-deaerated viscose then was extruded through a spinnerette with 3,000 holes of 0.0025-inch diameter each, into a primary acid coagulating-type spin bath containing 5.0 percent sulfuric acid, percent sodium sulfate and 3.0% zinc sulfate at a temperature of 40 C. The coagulated tow was wrapped around a godet and led through a hot secondary acid bath to a wash reel on which it was wrapped several times to prevent slippage.

The secondary acid bath contained about 3.0 percent sulfuric acid and residues of salts carried over from the primary bath. lt was maintained at about 9598 C, spinning speed was about 30 meters/minute and stretch through the secondary bath was 100 percent.

The tow was collected wet, cut into staple fiber lengths, washed, desulfurized, and fished in the usual manner with a staple fiber finish. After drying and conditioning, single filament tests were run under standard procedures.

Results of these tests are shown in Table 1 below, together comparable data for commercially produced super-crimp" rayon fibers.

A comparison of the properties of the two crimped fibers set forth in columns A and B of Table I shows the superiority of the tenacity, modulus and number of crimps of the rayon fibers of the invention over ordinary commercial crimped rayon fibers.

TABLE 1 A B Crimped Fiber commercial of the Invention "Super- Crimped Rayon Tenacity, g./d. Cond. 3.6 1.8 4 2.7 Wet 2.3 1.0 1.6 Elongation, Cond. 13.0 18 30 Wet 15.0 24 40 Wet Tenacity at 5% El. g./d. (Wet Modulus) 0.5 0.2 Crimps/inch 30 12 25 EXA M PLE II A modified viscose spinning solution was produced from alkali-treated chemical cellulose which was prepared by steeping a high purity, high DP wood pulp having uniform chain length distribution in 18.6 percent sodium hydroxide at 25 C. The thus formed alkali cellulose contained, after pressing, .35 percent cellulose and 15.2 percent sodiumhydroxide. The alkali cellulose was shredded and aged to a DP of about 500. It was then reacted with 34% carbon disulfide, based on the weight of cellulose, at 28 C-to form cellulose xanthate which was dissolved in sodium hydroxide at 10 C and mixed for 2 hours to produce a viscose solution containing 7.5 percent cellulose and 7.5 percent sodium hydroxide. To this viscose solution, 1.0 percent dimethylamine and 1.0 percent polyethylene glycol (both based on weight of cellulose) were added. The viscose solution was ripened to a salt (NaCl) index of 3.5.

The well-deaerated viscose then was extruded through a spinnerette with 3,000 holes of 0.0025-inch diameter each, into a primary acid coagulating-type spin bath containing 5.0 percent sulfuric acid, 15 percent sodium sulfate and 2.6 percent zinc sulfate at a temperature of 35 C. The coagulated tow was wrapped around a godet and led through a hot secondary acid bath to a wash reel on which it was wrapped several times to prevent slippage.

The secondary acid bath contained about 2.5 percent sulfuric acid and residues of salts carried over from the primary bath. It was maintained at about 98 C, spinning speed was about 40 meters/minute and stretch through the secondary spin bath was 95 percent.

The tow was collected wet, cut into staple fiber lengths, washed, desulfurized, and finished in the usual manner with a staple fiber finish. After drying and con ditioning, single filament tests were run under standard procedures.

The results of this testing showed that the fibers produced by the instant process had greater than 40 crimps (micro and macrocrimps) per inch with conditioned tenacity and elongation of 4.0 g/d and 12 percent, wet tenacity and elongation of 3.0 g/d and 14 percent and a wet modulus of0.55 g/d, respectively.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

We claim:

1. A process for producing highly crimped, high tenacity rayon filaments and staple fibers having average conditioned tenacity of about 3 to 4 g.p.d., wet modulus of about 0.4 to 0.6 g.p.d., wet tenacity of about 2 to 3 g.p.d., conditioned elongation of about 10 to 15 percent, wet elongation of about 12 to 18 percent and having greater than about 30 crimps per inch which comprises preparing a modified viscose spinning solution containing a mixture of viscose modifiers which substantially retard regeneration, said modified viscose solution having a salt (Na Cl) index of between about 2.5 and 6, spinning said modified viscose solution at a temperature of about 35 to 45 C into a coagulating-type spin bath, said coagulating-type spin bath containing from 4 to 6 percent by weight sulfuric acid, from 1 to 6 percent zinc sulfate and from 10 to 20 percent sodium sulfate, stretching the resulting coagulated, incompletely regenerated filaments as quickly and as much as possible without damaging the filaments prior to substantial regeneration and while the filaments are still substantially soluble in dilute alkali solution, the filaments being stretched up to about 120% in length, treating the filaments while they are being stretched with a dilute acid bath at a temperature of about 60 100 C, said acid bath containing about 0.5 5.0 percent sulfuric acid and a stabilized modicum of salts carried over from said coagulatingtype spin bath, immediately thereafter, completing the regeneration of the filaments and relaxing the tension on the filaments to permit crimp development, followed by washing and desulfurization of the resulting highly crimped filament or staple fiber product.

2. The process of claim 1 wherein said viscose modifiers comprise from 0.5 to 2.5 percent weight dimethylamine and from 0.5 to 2.5 percent by weight polyethylene glycol.

3. The process of claim 1 wherein travel of the filament through the coagulating-type spin bath is limited to that time required to develop sufficient strength to avoid unnecessary regeneration and wherein the greater percentage of stretch is achieved prior to substantial regeneration. 

1. A process for producing highly crimped, high tenacity rayon filaments and staple fibers having average conditioned tenacity of about 3 to 4 g.p.d., wet modulus of about 0.4 to 0.6 g.p.d., wet tenacity of about 2 to 3 g.p.d., conditioned elongation of about 10 to 15 percent, wet elongation of about 12 to 18 percent and having greater than about 30 crimps per inch which comprises preparing a modified viscose spinning solution containing a mixture of viscose modifiers which substantially retard regeneration, said modified viscose solution having a salt (Na Cl) index of between about 2.5 and 6, spinning said modified viscose solution at a temperature of about 35* to 45* C into a coagulating-type spin bath, said coagulating-type spin bath containing from 4 to 6 percent by weight sulfuric acid, from 1 to 6 percent zinc sulfate and from 10 to 20 percent sodium sulfate, stretching the resulting coagulated, incompletely regenerated filaments as quickly and as much as possible without damaging the filaments prior to substantial regeneration and while the filaments are still substantially soluble in dilute alkali solution, the filaments being stretched up to about 120% in length, treating the filaments while they are being stretched with a dilute acid bath at a temperature of about 60* - 100* C, said acid bath containing about 0.5 - 5.0 percent sulfuric acid and a stabilized modicum of salts carried over from said coagulating-type spin bath, immediately thereafter, completing the regeneration of the filaments and relaxing the tension on the filaments to permit crimp development, followed by washing and desulfurization of the resulting highly crimped filament or staple fiber product.
 2. The process of claim 1 wherein said viscose modifiers comprise from 0.5 to 2.5 percent weight dimethylamine and from 0.5 to 2.5 percent by weight polyethylene glycol.
 3. The process of claim 1 wherein travel of the filament through the coagulating-type spin bath is limited to that time required to develop sufficient strength to avoid unnecessary regeneration and wherein the greater percentage of stretch is achieved prior to substantial regeneration.
 4. The process of claim 1 wherein stretching takes place immediately after the onset of coagulation in a gradual manner. 